The interstitial stygobiotic isopods of the genus Microcharon (Crustacea) are diversified in Morocco. A new species, M. ourikensis, is described. The new species shows some original characters for this genus: large size, strong elongation in the first male pleopod exopodal inner lobe, 5-dentate mandibular pars incisiva, and 5 spines on the last mandibular palp segment. The species is a member of the Ibero-Maghrebin messoulii group. It is an endemic representative of the Ourika valley groundwater in the Moroccan High Atlas. It derives from a littoral marine ancestor which could have colonized the continental subterranean water during Turonian or Senonian Tethyan regressions.